U.S. Pat. No. 4,349,386 discloses mineral polymers called (sodium, potassium) polysialatesiloxo (referred to as NaKPSS in the patent) having the structural formula: ##STR1## where M is sodium or sodium plus potassium, n is the degree of polycondensation, and w has a value up to about 7. In order to form these NaKPSS polymers, anhydrous aluminum silicate and a mixture of strong alkali and alkali silicate are mixed in two stages. In the first stage, the reactant mixture is allowed to react at ambient temperature for at least an hour to form a viscous "mineral resin". See column 3, line 65 to column 4, line 2. In the second stage, the "mineral resin" is heated continuously or in stages at temperatures of about 25.degree. C. to 120.degree. C. for about 0.5 to 15 hours, depending upon the temperature of condensation, to further cure the mineral resin. See column 4, lines 13-25.
The patent indicates that the anhydrous aluminum silicate which is mixed with caustic and alkali silicate to form the mineral resin is prepared by calcining polyhydroxy-alumino-silicate (hydrated aluminum silicate) at temperatures of, for example, 550.degree. C. to 600.degree. C. to remove the water of hydration. See column 3, lines 20-24.
Example 3 of the patent discloses the use of a mineral resin, i.e. the partially cured polymers formed in the first stage by reacting at ambient temperature, to make a foundry mix. The patent indicates that the mineral resin is mixed with sand and allowed to further cure for several hours at ambient temperature or for approximately 1.5 hours at 85.degree. C.
In view of this data, it is clear that these polymers and this process are not practical to use in high production core and mold making processes under these conditions. In addition to their low strength and long setting time, these polymers, when used as foundry binders, have poor humidity resistance and require a high binder level (up to 6 to 7 weight percent based upon the weight of the sand) for effective use. Because of these deficiencies, foundry binders based upon these polymers are impractical to use for high production, heat-cured foundry applications.